We report relative proper motion measurements of H2O masers in massive star-forming region W51 Main, based on data sets of VLBI observations for H2O masers at 22 GHz with Japanese VERA telescopes from 2003 to 2006. Data reductions and single-beam imaging analysis are to measure internal kinematics of maser spots and eventually to estimate the three-dimensional kinematics of H2O masers in W51 Main. Average space motions and proper motion measurements of H2O masers are given both graphical and in table formats. We find in this study that W51 Main appears to be associated with hyper-compact H II region with multiple massive proto-stars whose spectral types are of late O.

• JaeSang Cho(Department of Astronomy, Yonsei University)
• Yukitoshi Kan-Ya(Department of Astronomy, Yonsei University/KASI/KVN, Yonsei University)
• Yong-Ik Byun(Department of Astronomy, Yonsei University)
• Tomoharu Kurayama(Faculty of Science and Engineering, Kagoshima University)
• Yoon Kyung Choi(Max-Planck-Institut fuer Radioastronomie Auf dem Huegel)
• Mi Kyoung Kim(Department of Astronomy, Graduate School of Science, The University of Tokyo)